1. Field of the Invention
The present invention generally relates to thermal conductive members, manufacturing methods of the thermal conductive members, heat radiating components, and semiconductor packages. More specifically, the present invention relates to a thermal conductive member used for radiating heat from a semiconductor element, a manufacturing method of the thermal conductive member, a heat radiating component using the thermal conductive member, and a semiconductor package using the thermal conductive member.
2. Description of the Related Art
A semiconductor element used for a CPU (Central Processing Unit) or the like is electrically connected and fixed onto a board in a semiconductor package. Since the semiconductor package has a high temperature at the time of operating, if the temperature of the semiconductor element is not decreased forcibly, not only full play is not given to the semiconductor ability, but the semiconductor element may be broken. Therefore, by providing a heat radiating plate (heat sink) or a heat radiating fin (or heat pipe) on the semiconductor element, heat generated by the semiconductor element is effectively radiated to the outside. The following structure has been suggested. That is, a TIM (Thermal Interface Material) is sandwiched between the semiconductor element and the heat radiating plate or the like, so that contact heat resistance is reduced due to the TIM following concave and convex surfaces of each of the semiconductor element and the heat radiating plate and thermal conductivity is thereby increased.
FIG. 1 is a cross-sectional view showing an example of a related art heat radiating component provided on a semiconductor package. In the semiconductor package, heat is generated by a semiconductor element 200 provided on a board 100. The heat is transferred to a heat radiating plate 400 via a thermal conductive member 300 provided on the semiconductor element 200. In addition, heat transferred to the heat radiating plate 400 is transferred to a heat radiating fin 500 via the thermal conductive member 300 provided on the heat radiating plate 400.
Thus, the thermal conductive member 300 is used as a part configured to efficiently and thermally connect the semiconductor element 200 and the heat radiating plate 400 to each other or the heat radiating plate 400 and the heat radiating fin 500 to each other.
Indium having a good thermal conductivity is frequently used as a material of the thermal conductive member 300. However, since Indium is a rare metal and expensive, there could be a future supply problem. Because of this, as another example of the thermal conductive member 300, silicon grease, an organic resin binder including a metal filler or graphite as a high thermal conductivity material, or the like is used. A resin molded sheet where carbon nanotubes are arranged in a thermal conductive direction has been known as the thermal conductive member 300. See Japanese Patent Application Publication No. 2008-258547, Japanese Patent Application Publication No. 2009-170828, and Japanese Patent Application Publication No. 2008-210954.
However, the thermal conductive member 300 made of the organic resin binder including the metal filler or graphite using resin as a binder may have a heat radiating capability problem because the thermal conductivity of the resin is not high. In addition, in the carbon nanotubes arranged in a thermal conductive direction, contact heat resistance between carbon nanotube end surfaces and the heat radiating component is large so that expected capabilities may not be realized. This is because short carbon nanotubes cannot reach the surface of the heat radiating component.
For example, FIG. 2 is a cross-sectional view showing an example of a contact surface of a thermal conductive member including a high thermal conductivity material and the related art heat radiating component. As shown in FIG. 2(a) and FIG. 2(b), the contact surface between the thermal conductive member 300a and the heat radiating plate 400 is rough in a microscopic view, and spaces 600 are formed between the contact surfaces of the thermal conductive member 300a and the heat radiating plate 400.
In an example shown in FIG. 2(a), the thermal conductive member 300a has a structure where an outermost surface of a high thermal conductivity material 302a is covered with a low thermal conductivity material layer 301a whose resin ratio is high. In this case, there is no physical contact between the heat radiating plate 400 and the high thermal conductivity material 302a such as metal filler or graphite, and the contact thermal resistance between the heat radiating plate 400 and the high thermal conductivity material 302a is large. Hence, the thermal conductivity may be low and the heat transfer may not be good.
In an example shown in FIG. 2(b), a thermal conductive member 300b has a structure where carbon nanotubes as high thermal conductivity materials 302b are fixed by a low thermal conductivity material layer 301b such as a resin binder. In this case, since there is great unevenness of the lengths of the high thermal conductivity materials 302b, short high thermal conductivity materials 302b do not reach the surface of the heat radiating plate 400. Hence, in this case, as well as the case shown in FIG. 2(a), the contact thermal resistance between the heat radiating plate 400 and the high thermal conductivity materials 302b is large. Hence, the thermal conductivity may be low and the heat transfer may not be good.